In response to the previous discussion of Keeping Up Appearances, I have to confess it to be the source of numerous hilarious family in-jokes, but only because my mother is obsessed with it. I suppose it's like watching a truly dreadful movie, but with a pack of moderately-drunk friends. Hilarity ensues!
Of course, I'm somewhat attached to Full House, myself, so any mockery of my mother's viewing weaknesses begs an introduction between Pot and Kettle. I began watching that show in the first grade. It was my very favorite. And even now, despite the shmaltzy morals and canned audience "awww"s, I still giggle at everyone's trite little catchphrases.
Nowadays, I think TV is crap. Nearly all of it. I don't own a television -- it just isn't worth it for me. I got to watch the first few seasons of the British Coupling on DVD, though, and I agree that they were brilliant. The character of The Melty Man was just... odd... but most of their freakish ideas panned out to comedic gold. I wish there were more shows like that.
Not a sitcom: Teenage Mutant Ninja Turtles! That show was freaking AWESOME!